The present invention relates to a rotary drill bit having a body with a projecting journal and a conical cutter having an axially recessed open end for receiving the journal wherein only the upper portion of the open cone mouth in the cavity formed between the cone and the body is shielded from drilled debris intrusion and the circulating air is channeled in the bearing to the bottom portion of the open cone mouth for an improved flow pattern through the various bearing segments whereby the incidence of plugging of the bit due to excess debris being forced into the bearing at the gaping open portion of the upper cone mouth is reduced.
Conventional rock bits which are employed for drilling wells and the like ordinarily employ two or three or more cone shaped rolling cutters rotatably mounted on journals, the cutters having teeth or rock crushing inserts on their conical surfaces. The cutters are so arranged as to roll, under considerable weight, upon the bottom surface of the hole being drilled as the well string to which the bit is attached is rotated. The cutters are mounted on the journals by interior, anti-friction bearings which are highly subject to wear and destruction if abrasive debris at the bottom of the well is allowed to penetrate between the journal and the cutter so as to contact the bearings.
Various means have been employed to combat this problem. For instance, many of the prior art devices use a seal at the exposed juncture of the journal and the open cone mouth to prevent migration of contamination inwardly to the bearings and to seal in lubricants. However, in such a system, as the seals wear, contamination which does enter the space between the cutter and the journal may bypass the seal and create a more rapid wear and destruction of the cutter bearings.
Other systems utilize a compressed fluid, such as air, which is forced through the journal to the lower most inner portion of the cutter bit thus forcing the air or fluid upwardly and outwardly in the passageways between the journal and the interior of the cutter head where the bearings are located not only to cool the bearings but also to force any contamination which gets into the interior of the cutting bit through the passageways to the exterior of the cutter bit at the cone mouth.
However, because of the construction of the bits which are attached to the body journals, a space or cavity is formed between the body and the upper portion of the cone mouth and drilling materials forced into the cavity under pressure tend to block it so that the fluid on the interior of the cutter bit cannot force materials out the upper portion of the cone mouth thus allowing the debris that accumulates there to gradually work its way to the interior of the bit thereby destroying it.
The present invention shields or blocks only the upper portion of the open cone mouth from drilled muck intrusion. The shield is formed preferably of spring steel but could also be a brush with very stiff bristles, a semi-porous mesh or other material which resists crush and permanent set. In a preferred embodiment, an arcuate spring steel shield extends for approximately 180.degree. about the journal and the cone mouth between the cone and the body in the upper semi-circle of the cone mouth and effectively blocks or prevents debris from entering this very vulnerable portion of the cone mouth. This blocking action is effected through the spring force of the shield which urges a curved portion of the shield against the rotating cone to block the space between the rotating cone and the body. In another embodiment, the contact of stiff brush bristles with the rotating cone is used to block the space between the rotating cone and the body. Thus, air, of other fluid which is forced through the journal to the interior of the cone, cannot exit at the upper portion of the cone mouth and therefore is forced to the lower portion and out there is less tendency for the muck to accumulate.
Thus, not only are the bearings effectively cooled and lubricated by the fluid but, by confining the exit area of the fluid to a limited area, the fluid pressure is also increased and the contamination is more effectively kept from entering the bearing. Further, the circulating air or fluid in the bearing which is forced to the bottom portion of the cone mouth provides for improved flow patterns through the various bearing segments and also reduces the incidence of plugging of the bit due to the excess formation being forced into the bearing at the gaping open portion of the upper cone mouth.